This invention generally relates to systems and methods for shutting down turbines and compressors. More particularly, the present invention relates to a system and method for shutting down a turbine and an associated compressor and for protecting the turbine and compressor through selective lubrication.
Turbines and compressors typically include rotating shafts supported by bearings. These rotating shafts and bearings generate friction heat that needs to be removed to maintain their physical integrity. Lubrication, generally oil, is supplied between the rotating shafts and bearings to remove the friction heat. Lubrication should continue during all operating phases to avoid shaft or bearing failures that lead to an unscheduled downtime.
The need for lubrication continues even after motive powers are removed from turbines and compressors in response to a shutdown request. Instead of stopping instantaneously, a rotating shaft gradually slows to a stop after a motive power is removed. For example, a rotating shaft in a steam-driven turbine continues to rotate for a period of time after the steam supply to the turbine stops. Likewise, a rotating shaft in an electric-motor-driven compressor continues to rotate for a period of time after the electric power is removed. Thus, turbines and compressors need lubrication until their rotating shafts slow to a stop in response to a shutdown request.
One conventional approach to meet this need is maintaining lubrication for a fixed period of time after a shutdown request. In this conventional approach, one estimates the time for a rotating shaft to stop and then sets the fixed period of time based on the estimated time. This approach, however, does not ensure that a rotating shaft receives lubrication while it is rotating. In other words, lubrication to a rotating shaft ceases at the end of a fixed period of time regardless of the actual time for the rotating shaft to stop. Therefore, a rotating shaft and its corresponding bearing may be physically damaged if, for any reason, it rotates after the fixed period of time.
Accordingly, an object of the present invention is directed to an improved system and method for protecting during a shutdown a turbine and a compressor driven by a turbine shaft, particularly a turbine and associated compressor used in a refrigeration, air-conditioning, or heat pump system. The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention is directed to a system for protecting during a shutdown a turbine having a turbine shaft and a compressor driven by the turbine shaft. The system includes a first lubrication system, a second lubrication system, and a control system. The first lubrication system is configured to provide lubrication to the compressor. The second lubrication system is configured to provide lubrication to the turbine. The control system monitors the rotation of the turbine shaft in response to a shutdown request and causes the first and second lubrication systems to provide lubrication to the turbine and compressor until and after the turbine shaft stops rotating.
In another aspect, the invention is directed to a method for protecting during a shutdown a turbine having a turbine shaft and a compressor driven by the turbine shaft. The method includes the steps of: (a) initiating the shutdown of the turbine and compressor; (b) monitoring the rotation of the turbine shaft; (c) providing lubrication to the turbine and compressor until the turbine shaft stops rotating; and (d) providing lubrication to the turbine and compressor after the turbine shaft stops rotating.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.